As far as I know, there is no limit, as bitbucket is not a rapidshare-alike thing, but a very geneorus (sic) hosting to programming projects managed with Mercurial.
Mercurial is a SVN, GIT, CVS... alternative. It works pretty well and I am using it to some php projects, too.
Firefox itsefs is managed using Mercurial, (but not hosted in bitbucket).
So, I think the only risk of that account being terminated would be the shutdown of the site.
PD: There is a Windows shell extension to manage HG repositories (HG = Mercurial). It is TortoiseHG and it's hosted in bitbucket, too.http://bitbucket.org/tortoisehg/stable/wiki/Home